3.5.4.2. How Much Carbon Can Be Sequestered by Global Afforestation and Reforestation?

As Table 3-17 shows, afforestation and reforestation
potentially could achieve annual carbon sequestration rates in aboveground and
below-ground biomass of 0.4-1.2 t ha-1 yr-1 in boreal regions, 1.5-4.5 t ha-1
yr-1 in temperate regions, and 4-8 t ha-1 yr-1 in tropical regions (Dixon et
al., 1994; Nabuurs and Mohren, 1995; Nilsson and Schopfhauser, 1995; Brown
et al., 1996; Yamagata and Alexandrov, 1999). The latter two values assume
that there is 0.3 t C m-3 of wood in boreal and temperate regions and 0.4 t
C m-3 wood in tropical regions (Nilsson and Schopfhauser, 1995). The maximum
amount of carbon that might be sequestered by global afforestation and reforestation
activities for the 55-year period 1995-2050 was estimated at 60-87 Gt C, with
about 70 percent in tropical forests, 25 percent in temperate forests, and 5
percent in boreal forests (Brown et al., 1996). Hence, an average maximum
potential carbon sequestration rate would be 1.1-1.6 Gt yr-1 above and below
ground (Brown et al., 1996). Although these maximum values represent
about 2 percent of the annual global carbon uptake by the terrestrial biosphere,
they are much higher values than would be expected from ARD activities in all
but the most broadly defined ARD lands (e.g., FAO or Land Cover definitional
scenarios).

Table 3-17: Estimate of accounted average
annual carbon stock change for ARD activities. The IPCC and FAO Definitional Scenarios
and three accounting approaches under the FAO Definitional Scenario have been
applied to illustrate with the available data the effect of different accounting
approaches. Other Definitional Scenarios described in Table
3-4 have not been included in this analysis. It is assumed that recent area
conversion rates ["recent" = for Annex I Parties AR late 1980s/early 1990s and
for D 1980s (except for Canada and Russian Federation early 1990s); ARD in other
regions 1980s] have applied since 1990 and will continue to do so through the
first commitment period. It is also assumed that current uptake rates apply during
the first commitment period. The figures and ranges of values in the table are
illustrative and provide first-order estimates, and may not encompass the full
range of uncertainties. Negative numbers indicate carbon emissions and positive
numbers carbon removals.

Includes carbon in aboveground and below-ground biomass,
excludes carbon in soils and DOC

Region

Activity

Rate of Uptaked
(t C ha-1 yr-1);
D Average Stocka,d
(t C ha-1)

Post-Harvest
Regeneration

Conversion
between
Non-Forest
and Forest

FAO Definitional
Scenario
Land-Based I
Accountingb

FAO Definitional
Scenario,
Land-Based II
Accountingb

FAO Definitional
Scenario,
Activity-Based
Accountingb

IPCC
Definitional
Scenariob

Boreal Region

AR

0.4 0.8 1.2

3.1e

0.1e

R: -209 -191 -164
A: 0.2 0.7 1.6
-18
-227 -208 -180

R: -56 -38 -10
A: 0.2 0.7 1.6
-18
-74 -55 -26

R: 5 21 46
A: 0.2 0.7 1.6
-18
-13 4 30

AR: 0.2 0.7 1.6

-18
-18 -17 -16

Total (= Annex I)g

D
Total ARD

35

0.5e

Temperate Region

AR

1.5 3 4.5

5.4e

0.5e

R: -557 -351 -125
A: 7 25 44
-72(j)
-622 -398 -153

R: -141 49 259
A: 7 25 44
-72j
-206 2 231

R: 74 265 475
A: 7 25 44
-72j
9 218 447

AR: 7 25 44

-72j
-65 -47 -28

Annex Ig

D
Total ARD

60

1.2e,i

Annex I Totalg

AR

8.5e

0.6e,i

R: -766 -542 -289
A: 7 26 46
-90
-849 -606 -333

R: -197 11 249
A: 7 26 46
-90
-280 -53 205

R: 80 289 527
A: 7 26 46
-90
-3 225 483

AR: 7 26 46

-90
-83 -64 -44

D
Total ARD

1.7e

Temperate Region

AR

1.5 3 4.5

n/a

1.9f,i

R: n/a
A: 27 93 167
-126
n/a

R: n/a
A: 27 93 167
-126
n/a

R: n/a
A: 27 93 167
-126
n/a

AR: 27 93 167

-126
-99 -33 41

Total

D
Total ARD

60

2.1c

Tropical Region

AR

4 6 8

n/a

2.6f

R: n/a
A: 170 305 415
-1644
n/a

R: n/a
A: 170 305 415
-1644
n/a

R: n/a
A: 170 305 415
-1644
n/a

AR: 170 305 415

1644
-1474 -1339 -1229

Total

D
Total ARD

120

13.7c

Global Total

AR

n/a

4.6

R: n/a
A: 197 399 584
-1788
n/a

R: n/a
A: 197 399 584
-1788
n/a

R: n/a
A: 197 399 584
-1788
n/a

AR: 197 399 584

-1788
-1591 -1389 -1204

(summing regional totals)

D
Total ARD

16.3

n/a = Area of regeneration after harvest not available. In addition, regeneration
after selective cutting, as is often used in tropics, is difficult to capture
with the FAO Definitional Scenario.

aLiterature sources do not allow estimation of uncertainty levels of carbon
stocks prior to deforestation or of areas deforested. bThe values under the three accounting approaches of the FAO Definitional
Scenario and in the IPCC Definitional Scenario were calculated with a spreadsheet
that includes all relevant cohorts of the landscape subject to ARD activities,
based on the following assumptions. (1) Trees grow according to a sigmoidal
growth curve with a maximum mean annual increment at the time of harvest ("Average
Uptake Rate" in the table). (2) The biomass stock (aboveground and below-ground
biomass, but not soil carbon) just before harvest is twice the "D Average Stock"
in boreal and temperate regions and 1.33 times in the tropical regions. This,
in combination with the growth rates in the table, results in rotation cycles
of 175, 88, and 58 years for the boreal region; 80, 40, and 27 years for the
temperate region; and 40, 27, and 20 for the tropical region. (3) One-third
of the biomass stock at harvest is assumed to be left on the site as slash,
litter, and dead roots. This material is assumed to decay at a constant rate
in 15 years (boreal), 10 years (temperate), and 5 years (tropical).
The IPCC Definitional Scenario includes transitions between forest and non-forest
land uses under Article 3.3. The FAO Definitional Scenario includes the harvest/regeneration
cycle, because regeneration is defined as reforestation. Within the FAO Definitional
Scenario we distinguish three accounting approaches. Land-based I approach always
accounts for stock changes over the full commitment period. Land-based II approach
starts the accounting in 2008 or with the activity, whichever is later. Stock
changes that do not result from reforestation (e.g., decay of post-harvest slash)
are counted. The activity-based approach is the same as land-based II except
that stock changes in decaying slash from a preceding harvest are excluded.
The results for R in FAO land-based I approach are negative because the stock
changes due to harvest dominate the carbon balance. The stock-change values
under FAO land-based II approach are negative in boreal Annex I Parties and
range from negative to positive numbers for temperate Annex I Parties depending
on how quickly stand growth increases after harvest to offset the loss of carbon
from decaying materials. The large positive values shown for FAO activity-based
accounting arise because none of the carbon-stock losses are accounted whereas
the carbon gains from biomass growth are. In the IPCC Definitional Scenario
no initial harvest occurs and therefore there is no difference between the accounting
approaches-only one set of numbers is shown. Sigmoidal growth curves as used
in the calculations provide lower uptake in the early and late stand development
compared to linear growth curves, but higher uptake in between.
Stock changes from deforestation are calculated as the average stock multiplied
by the recent annual rate of deforestation. For example, annual deforestation
of 1.2 Mha in temperate region (with 60 t C ha-1) results in annual emissions
of 72 Mt C yr-1. cFAO (1996) and Brown et al. (1996) estimate deforestation in developing
countries between 1980 and 1990 at 16.3 Mha yr-1 (15.4 Mha yr-1 in the tropics).
A critique of the methods and database sources with which these estimates were
derived can be found at <http://www.fao.org/forestry/for/fra/FO124E/GEP15>.
A more recent number for deforestation between 1990 and 1995 is lower at 13.7
Mha yr-1 (FAO, 1999) and has been used here. The older number from FRA 1990
(FAO, 1996) is not comparable with this new number from FAO (1999) because:
(i) The two data sets are completely different; (ii) the FRA data sets are updated
for new data becoming available after an assessment; and (iii) the data set
for the period 1990-1995 (FAO, 1999) still has some gaps (FAO, 2000). It is
recommended that definitive conclusions be drawn based on the forthcoming new
statistics from the Forest Resource Assessment 2000, which should become available
during the year 2000 (FAO, 2000). dUptake rates are intended to span the range within which the average value
for each region is expected to be. These numbers were derived from the sources
below, some of which (e.g., Nilsson and Schopfhauser, 1995) give country- or
region-specific data, thus allowing to calculate a weighted mean. Uptake rates
and carbon stocks given include aboveground and below-ground biomass, but not
soil carbon or dead organic matter (DOC). "D Average Stock" is an average over
the landscape, assuming that D will equally impact all age classes of the forest
estate. All these values include total biomass but exclude carbon in wood products,
DOC, and soil carbon (except FAO land-based II approach which factors in post-harvest
slash). Average rate of uptake are from Dixon et al. (1994), Nabuurs and Mohren
(1995), Nilsson and Schopfhauser (1995), Brown et al. (1996), and Yamagata and
Alexandro (1999); average stock for boreal and temperate regions are from TBFRA
2000 (UN, 1999), for tropics from Dixon et al. (1994), supported by Table
1 in the SPM. The number for the tropics may be regarded to be a high estimate,
but was used here in absence of additional literature sources. eAreas as given in Table 3-14. Extension
of forest is used to approximate the area of afforestation and reforestation
under the IPCC Definitional Scenario and the area of afforestation under the
FAO Definitional Scenario. Regeneration is used to approximate the area of reforestation
under the FAO Definitional Scenario. Loss to other uses is used to approximate
the area of deforestation.
Recent AR area estimates for Annex I Parties are data from the TBFRA 2000 (UN,
1999), and D area estimates from FRA 1990 (UN-ECE/FAO, 1992). D for Russian
Federation is from A. Shvidenko (pers. comm.). D for Canada is from Robinson
et al. (1999). Data for Australia are based on NGGI (1999). fFAO (1995). This estimate should be regarded as an upper limit, because
some countries may have reported plantations for 1990 but not for 1980, and
because some of the plantations may not qualify as resulting from AR activities
under the IPCC Definitional Scenario.gBoreal Annex I countries included: Canada, Finland, Iceland, Norway, Russian
Federation, and Sweden. Temperate Annex I countries included: Australia, Austria,
Belarus, Belgium, Bulgaria, Croatia, Czech Republic, Denmark, Estonia, France,
Germany, Hungary, Ireland, Italy, Japan, Latvia, Liechtenstein, Lithuania, The
Netherlands, New Zealand, Poland, Portugal, Slovakia, Slovenia, Switzerland,
Turkey, Ukraine, United Kingdom, and United States of America. Data for Greece,
Luxemburg, and Spain were not available. hBecause of the average uptake rates and carbon stocks at harvest that were
used in this table, stands planted or regenerated since 1990 are not harvested
before the end of the commitment period in the calculations. However, there
may be AR forests with a very short rotation that are harvested in the first
commitment period. The accounting for such stands may require a deduction of
the harvested stock from the reported stock change. See Section
3.3.2.2, item b3. iThe regeneration area for the United States of America in UN (1999) is 1.8
Mha yr-1. However, this number is incorrect and has been replaced with a corrected
number of 0.2 Mha yr-1 (US Forest Service, 2000). jThese results do not take into account the effect of the second sentence
of Article 3.7 of the Kyoto Protocol.

Note that the annual carbon sequestration value is not constant; it will vary
from year to year with annual weather conditions and would change over longer
terms. Nilsson and Schopfhauser (1995) calculated a mean annual global carbon
increment of 0.4 Gt C yr-1 above ground, with an additional 0.1 Gt C yr-1 below
ground, from potential afforestation and deforestation 20 years after initiation
of an optimum set of global forest plantations. Neither the value derived from
Brown et al. (1996) nor that from Nilsson and Schopfhauser (1995) included
carbon losses to deforestation or degradation from tropical fuelwood extraction
(Alcamo et al., 1996; Solomon et al., 1996), from deteriorating
climate, or from increasing agriculture (Cramer and Solomon, 1993; Alcamo et
al., 1996).

The FAO scenario (with the activity-based approach) and the IPCC scenario produce
different estimates of potential carbon stock changes. Under the IPCC definitional
scenario, if Annex I countries (approximated by the estimates for boreal and
temperate region Annex I countries in Table 3-17) maintain
recent rates of afforestation and reforestation from 1990 through 2012, the
estimated rate of increase in carbon stocks from these activities would be 7-46
Mt C yr-1. Under the same assumptions, this increase would be offset by estimated
decreases in carbon stocks from deforestation of 90 Mt C yr-1, producing a net
change of -83 to -44 Mt C yr-1. Under the FAO definitional scenario using the
activity-based accounting approach (i.e., the stock change accounting does not
start before the activity, nor does it include carbon loss from decaying slash),
if Annex I countries maintain recent rates of afforestation and reforestation
from 1990 through 2012, the estimated rate of increase in carbon stocks from
these activities would be from 87-573 Mt C yr-1, with estimated decreases in
carbon stocks from deforestation of 90 Mt C yr-1-producing a net change of -3
to 483 Mt C yr-1. Under the FAO scenario using land-based accounting approach
I, the estimated stock change from afforestation and reforestation activities
continued at recent rates would be -759 to -243 Mt C yr-1 and from deforestation
activities -90 Mt C yr-1, resulting in an estimated net stock change of -849
to -333 Mt C yr-1. Under the FAO scenario using land-based accounting approach
II, the estimated stock change for afforestation and reforestation activities
continued at recent rates would be -190 to 295 MtC yr-1 and from deforestation
activities -90 Mt C yr-1, resulting in an estimated net stock change of -280
to 205 Mt C yr-1.

Under the IPCC definitional scenario, if recent rates of afforestation and
reforestation are increased by 20 percent and rates of deforestation decreased
by 20 percent in Annex I countries from the year 1990, carbon stocks would increase
by 7-49 Mt C yr-1 due to afforestation and reforestation activities and decrease
by 72 Mt C yr-1 due to deforestation activities, resulting in a net change in
carbon stocks from these activities of -83 to -23 Mt C yr-1 in Annex I countries.
For comparison purposes, increases in carbon stocks from afforestation and reforestation
globally using the IPCC definitions could result in a stock change of about
197-584 Mt C yr-1 and decreases from deforestation of about 1,788 Mt C yr-1
if current rates are maintained.

In the IPCC Definitional Scenario and FAO Definitional Scenario with land-based
I accounting approach, the accounted carbon stock changes are broadly consistent
with the 2008-2012 actual changes in carbon stocks from land under Article 3.3.
The IPCC and FAO Definitional Scenarios bring different amounts of land under
Article 3.3, hence the estimated carbon stock changes in Table
3-17 differ. In the FAO Definitional Scenario with land-based II and activity-based
accounting approaches, the accounted carbon stock change is not consistent with
the 2008-2012 actual changes in carbon stocks on land under Article 3.3, except
in the case of short rotation cycles. In neither of the two Definitional Scenarios
is the accounted carbon stock change consistent with the 2008-2012 actual carbon
stock changes, nor with the net exchanges with the atmosphere, at the national
and global levels in part because the land under Article 3.3 is small in comparison
with the national and global forest area (see Section 3.5.2.5).